How to find digits after decimal? [closed]

问题

I want to write a program in C++ to cin a Decimal number and cout the digits after Decimal for example 0.26547 -> 5.

I wrote this but not work correctly:

       int main()
 {
 int i=0,b;
float a ;
  cin>>a ;
   while(a!=0)
  {
    a*=10 ;
    b=a ;
    a-=b ;
    i+=1 ;
 }
 cout<<i ;
 }

For example for 0.258 instead of 3, returns 20. can one explain me what is the problem of this code ? thank you

回答1:

C++ permits decimal representation of floating point numbers, but as far as I know all extant implementations use binary representation. And then the idea of storing the user's decimal number specification as a floating point value, loses critical information about the decimal digits: they're simply not there any more. So to count the decimal digits in the specification, you have to store it as a string.

Pseudo-code:

input number specification as a string, e.g. using getline.
verify that it's a valid number specification, e.g. using stod.
scan for the first period from the right, call this position P.
scan for the maximum number of decimal digits from position P.

回答2:

I am unsure why your code does not work (What compiler are you using?), but I think it might related to

b=a;

Try explicitly casting your float to an int

b = int(a);

Alternatively, you could choose not to use an int, and round a float down using the function floor by including math.h #include <math.h>

float a = 5.9f;
float b = floor(a);
a -= b;

来源：https://stackoverflow.com/questions/41197139/how-to-find-digits-after-decimal

标签

c++

decimal